Abstract:The iridophore is a kind of common pigment cell in teleosts. It contains a large number of iridosomes, which contain reflecting platelets with high refractive index composed of guanine crystals. The reflecting platelets and the cytoplasm with low refractive index are alternately arranged to form alternating layers. After light is reflected by the alternating layers, the iridophores show an iridescent color through multilayer thin-film interference. Iridophores achieve color change by changing the distances between each of the reflecting platelets under the stimulation of hormones, sympathetic nervous system or external environment factors. Guanine is the basis for the coloration and color changes of iridophores, and its biosynthesis pathway has been analyzed in detail. Iridophores are differentiated from multipotent neural crest cells. The lineage specialization process of differentiation from neural crest cells to mature iridophores requires multiple genes. At present, some key genes have been found in the model organism, zebrafish, and the core gene regulatory network governing iridophore specification has been preliminarily analyzed through studying the interactions among those genes. At the same time, other genes and signaling pathways affecting the specialization, differentiation and survival of iridophores have also been found. This manuscript reviews advances of studies in the mechanism of coloration and color change of iridophores, the pathway and genes involved in guanine biosynthesis, as well as genes and signaling pathways affecting the development and survival of iridophores in teleosts. Prospects for future research directions are also provided. It is aimed at a deeper understanding of iridophores and providing a reference for studying gene regulation during iridophore development.

Abstract:The rise of intensive aquaculture in recent year has led to frequent occurrence of fish diseases, with the increased morbidity and mortality in juvenile fish posing a particularly serious threat to the development of the industry. Accordingly, how to protect the health of juvenile fish has become an urgent problem for the development of aquaculture. Probiotics can promote the growth and development of juvenile fish by resisting pathogens and water pollutants, promoting the uptake of nutrients, regulating the immune system, modulating intestinal microorganisms, and enhancing intestinal barrier of juvenile fish. However, the mechanisms related to such processes still require further exploration. This review summarizes the beneficial effects of probiotics on juvenile fish development and their possible mechanisms. We also address the challenge of the probiotics in juvenile fish farming, which may provide valuable information for the application of probiotics in juvenile aquaculture.

Abstract:Grass carp (Ctenopharyngodon idella) are susceptible to grass carp reovirus (GCRV) and exhibit severe hemorrhage when infected. In contrast, Squaliobarbus curriculus (Sc) are resistant to GCRV. We have generated C. idella/S. curriculus hybrid fish which are relatively more resistant to GCRV than C. idella. These fish populations provide valuable resources for investigating the genetic mechanisms of the antiviral immunity. The laboratory of genetics and physiology 2 (LGP2) is a member of RIG-Ⅰ like receptor family and is involved in recognition of viral nuclear acid at the first line of defense. Understanding its functions in antiviral immunity will have a significant impact on the molecular breeding of fish with resistant traits. In this study, the full-length cDNA (2 940 bp) and the 5′ upstream sequence (721 bp) of the S. curriculus lgp2 (Sclgp2) gene were sequenced. The 5' upstream region contains several putative transcription factor binding sites for MafB (muscle aponeurosis fibromatosis B) and IRF3 (interferon regulatory factor 3). The Sclgp2 encodes a protein of 680 amino acids which consists of conserved DEXD/H (DExD/H-box helicase domain), HELICc (helicase superfamily C-terminal domain) and CTD (C-terminal regulatory domain). The functional domains and the number of predicted phosphorylation sites are similar to that in other fish species, with differences in domain arrangement and amino acid sequences. Furthermore, by comparing the sequences of C. idella and S. curriculus LGP2 proteins, two GCRV sites associated with GCRV resistance in the RNA binding region were identified. In the phylogenetic tree, ScLGP2 was clustered in a clade containing the homologs from C. idella, Carassius auratus and Mylopharyngodon piceus, forming an expanded clade with the homologs from other cyprinid fish. Quantitative PCR analysis revealed that the mRNA expression level of Sclgp2 was the highest in the spleen, followed by muscle and heart, whereas the lowest was detected in the intestine. The expression levels of Sclgp2 and ifn1 remained unchanged in most tissues except that the ifn1 expression was significantly down-regulated in the liver at 24-72 h after GCRV infection. Interestingly, the mRNA expression levels of Sclgp2 in the muscle positively correlated with that of ifn1 (0.999, P<0.01). ScLGP2 weakly interacted with ScMDA5, yet DEXDc (1-201 aa), HELICc (390-476 aa) and CTD (553-668 aa) were not engaged in such interaction. Taken together, the present study provides basis for studying the functions of ScLGP2 and exploring the Sclgp2 gene as a potential marker for genetic breeding of disease resistant C. idella.

Abstract:In order to explore the effects of low temperature stress on intestinal oxidative stress, apoptosis and intestinal microbial composition of Takifugu fasciatus, experiments were conducted to measure oxidative stress, apoptosis and intestinal microbe-related indicators at 3 treatment temperatures (25, 19 and 13 °C) and 4 sampling time periods (0, 6, 24 and 96 h). Compared with the control group, the results showed that as the temperature decreased, intestinal villi underwent necrosis, hyperplasia and enlargement of goblet cells, the enzymatic activities of total superoxide dismutase (T-SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and the content of malondialdehyde (MDA) increased significantly, while the diversity of gut microbial composition decreased. Changes in gut microbial abundance, such as Xanthobacter, Paracocuus, Lactococcus, and Bididobacter increased with decreasing temperature, Clostridium, Aeromonas and Geobacillus decreased with increasing temperature, and the expression of apoptosis-related genes (caspase3, caspase7, caspase9, p53, Bax, Bcl-2) increased with the decrease of temperature. In addition, we found that the alterations in the abundance of Paracocuus and Geobacillus had Pearson correlations with intestinal oxidative stress and apoptosis, which may be potential microbes to reflect whether the T. fasciatus is in a state of oxidative stress and apoptosis. The results of this study provide reference for the healthy breeding of T. fasciatus.

Abstract:The rapid development of marine aquaculture in China, especially that of raft shellfish culture, not only contributes directly to China’s economic benefits, but also facilitates fishery resources conservation to a certain extend. Large-scale raft culture, in a sense, has played a role of artificial floating reefs, providing temporary or permanent feeding or sheltering habitats for fish, which coincides with the core idea of marine ranch development based on floating reef systems. Fish assemblages and their community characteristics in raft mussel farming habitats play key roles in understanding functions of floating artificial reef system in marine ranching area. Hence, fish composition and community structure in surface and bottom levels of a mussel farming habitat in Gouqi Island waters and an adjacent rocky reef habitat were analyzed based on data collected by multi-mesh trammel nets from September to December 2020. Index of relative importance (IRI), species diversity indices and non-metric multidimensional scaling (nMDS) analysis were used. A total of 55 fish species belonging to 47 genera in 34 families of 10 orders were collected from two habitats. Among which, 37 species were collected from mussel farming habitat, including 29 species from bottom level and 20 species from surface level; 40 species were collected from rocky habitat. In terms of dominant species composition, Lateolabrax maculatus and Mugil cephalus were the typical dominant species in the surface level of mussel farming habitat, while Nibea albiflora and Sebastiscus marmoratus were the typical dominant species in the bottom level of mussel farming habitat. S. marmoratus was also a typical dominant species in the reef habitat. The similarity analysis showed that the similarity in species composition between the surface and bottom level of mussel farming habitat and the reef habitat was below a moderate level of dissimilarity. Diversity analysis showed that the overall diversity of mussel farming habitat was higher than that of rocky reef habitat, but not significantly (P>0.05). The multivariate analysis indicated that fish community could be grouped into three types in the two habitats, though it was not strictly consistent with the surface area, bottom area and reef area. Results of ANOSIM suggest that there was significant difference among grouped communities (P<0.05). Our study suggests the following: ① the presence of large-scale raft culture facilities in rocky island waters attract many pelagic and demersal fishes, providing additional habitat for dominant rocky fishes, among which S. marmoratus, N. albiflora, M. cephalus and L. maculatus could be suitable target species in the marine ranching programs of northern East China Sea; ② mussel farming habitat and nearshore rocky reef habitat have obvious complementary and gain of habitat functions, which play essential roles on protection of common commercial fish populations in the East China Sea and comprehensive conservation of local fish in different life stages. It is hoped that this study may contribute to technology as well as target fish selection in marine ranching programs and the application of artificial habitat construction model carried out in island waters.

Abstract:While silver croaker (Pennahia argentata) is an economically and ecologically important species in the East China Sea, researches on its life history traits, stock assessment and fishery management are limited in recent years. Given the increasing fishing intensity and great changes of ecosystem, limited studies of P. argentata would lead to misunderstanding of its stock status and difficulties in its conservation and management. Based on samples from the scientific survey in the offshore waters of southern Zhejiang in 2016, this study intends to understand the life history of P. argentata (growth, maturity, and mortality), to evaluate the stock status and to provide management advice. This study analyzed the life history traits based on the widely used and empirical methods, i.e. von Bertalanffy growth function for growth parameters, logistic maturity curve, and Pauly empirical formula for mortality coefficients. The yield per recruitment (YPR) and spawning stock biomass per recruitment (SSBR) models were constructed, considering the influence of natural mortality and selectivity. The asymptotic length of P. argentata was estimated to be 25.36 cm, and the exponential rate was 0.32 in the growth function. The current length of 50% selectivity (13.52 cm) was much smaller than the length of first sexual maturity (17.79 cm). Based on the length-converted catch curve, the total mortality of P. argentata was estimated to be 2.62. The Pauly empirical formula estimated the natural mortality M to be 0.74, while the fishing mortality estimate was 1.88. Results of YPR and SSBR models revealed that the biological reference points F_max and F_0.1 were 3.43 and 0.78, while F_20% and F_40% were estimated to be 0.66 and 0.33, respectively. The current fishing intensity was much higher than F_20%, indicating recruitment overfishing for this stock. Scenarios considering different natural mortality (M=0.54, 0.64, 0.74, 0.84 and 0.94) and different selectivity (age of 50% selectivity: t₅₀=1.47,1.77, 2.07, 2.37 and 2.67), were evaluated in the sensitivity analysis for YPR and SSBR models. When M increased from 0.54 to 0.94, the estimates for the current YPR would decrease from 17.69 to 10.48, and the current SSBR would slightly decrease from 0.82 to 0.57. When the t₅₀ increased, both YPR and SSBR declined in different degrees. Both YPR and SSBR, including the biological reference points, were sensitive to M and selectivity. The stock of P. argentata. in offshore waters of southern Zhejiang has been recruitment overfished in 2016, and both natural mortality and selectivity have substantial influence on the stock assessment and management advices for this fishery. Therefore, it is recommended to reduce the fishing intensity and increase the first capture length in order to improve the conservation and management of P. argentata.

Abstract:The pike-perch (Sander lucioperca) is a native fish species in European and Asian river basins. Owing to its fast growth rate, strong adaptability, and high nutritional value, it has become a promising candidate species for aquaculture. In China, artificial reproduction of pike-perch has been realized, and most of its parents are caught from wild populations. However, the genetic background and diversity information of wild populations are still limited, which is not conducive to the establishment of genetic breeding management strategies. In order to investigate the genetic structure of S. lucioperca wild populations, we analyzed the genetic differences of six populations in China and two populations in Central Asia using partial mitochondrial COⅠ gene sequences, and compared them with the haplotype sequences of European populations. As a result, 5 variable sites were detected in the 640 bp COⅠ gene sequence, and 7 haplotypes were defined, among which Hap1 was the shared haplotype between eight populations, and was identical to HapA of European groups. The proportion of Hap1 in Chinese populations (93.36%) was higher than that in Central Asian populations (72.58%) and European population (55.56%). Hap2 and Hap3 were specific haplotypes of Chinese populations, while Hap4, Hap5, Hap6, and Hap7 were specific haplotypes of Central Asian populations. The cluster and network analysis of haplotype sequences showed that Hap1/A was the ancestral haplotype in Sander lucioperca populations. The specific haplotype of Chinese and Central Asian populations belonged to Hap1/A subtype with only 1-2 loci variation compared with the ancestral haplotype, which was quite different from the specific haplotype of European populations. The number of haplotypes per population ranged from one to four, with the largest number of haplotypes in the Zaysan Lake (ZS) population, while there was only one haplotype (Hap1) in Tengger Lake (NX), Xingkai Lake (XK) and Yalu River (YJ) populations in China. The haplotype diversity (H_d) and nucleotide diversity (π) of TS population were the highest (H_d=0.514±0.069; P_i=0.000 80±0.000 11), followed by ZS population, while the diversity parameters of six populations in China were lower. The AMOVA analysis showed that the genetic variation among S. lucioperca populations accounted for 20.74%, and the degree of genetic differentiation (F_st) among populations was relatively high (0.15≤F_st=0.207 36<0.25). The genetic differentiation of the TS and the ZS, the TS and the six Chinese populations all were great (F_st>0.25). Among Chinese populations, Heihe (HH) population had great genetic differentiation against other populations, while there was no genetic differentiation between the other five populations. The phylogenetic tree based on genetic distance showed that six populations from China and ZS population from Kazakhstan were clustered into one branch, while TS population from Uzbekistan was a separate branch. The results of this study provide a reference for the breeding and releasing management of S. lucioperca populations.

Abstract:The transition from planktonic larva to benthic juvenile is a critical period for decapod crustaceans. If the habitat was suitable, the post-larval individuals will quickly settle down. In addition, individuals in different development stages may choose different habitats. Chinese mitten crab (Eriocheir sinensis) is an important economic species in China. The juvenile E. sinensis mainly live in the intertidal zone of the Yangtze Estuary, but there is no systematic study on its habitat selection patterns. Therefore, in order to explore the habitat preference of E. sinensis larvae, simulation experiments of four habitats common on Yangtze Estuary, namely Scirpus mariqueter, mud bottom, consolidated silt and gravel, were conducted in the laboratory. In addition, behavior observation and quantitative analysis of the megalopa, juvenile of E. sinensis (at stages Ⅰ, Ⅲ and Ⅴ) were carried out in different habitats. The results showed that there were significant differences in the distributions of the four stages in the four habitats (Kruskal-Wallis test, P < 0.05). The distribution proportions of megalopa (73.7%±6.8%), stage Ⅰ juvenile (78.2%±8.8%), stage Ⅲ juvenile (53.6%±8.0%) and stage Ⅴ juvenile (54.8%±6.8%) in the S. mariqueter habitat were significantly higher than other habitats (P < 0.05). The proportions of stage Ⅲ and Ⅴ juvenile in mud and consolidated silt were significantly higher than other stages (P<0.05). Juveniles had swimming, cling, epibiosis and burying behaviors in S. mariqueter habitat. Megalopa and stage Ⅰ juvenile showed cling behavior, accounting for 82.1%±5.1% and 83.3%±8.7% of the group, respectively. Only megalopa showed swimming behavior (9.0%±3.7%). For stage Ⅲ, epibiosis (44.2%±17.9%) and burying rate (36.5%±16.7%) were significantly increased (P<0.05). In addition, since it is difficult to observe the stage Ⅴ juvenile, the behavior experiment of stage Ⅴ juvenile showed no results. Figure 4 shows the cumulative percentage of molting and mortality rates of juveniles within 5 days. Feeding and habitat had significant effects on the molting rate (feeding: F=166.48, P<0.05, habitat: F=198.09, P<0.05), and the interaction between them was significant (F=21.84, P<0.05). The juveniles were found to show significantly higher molting rate in S. mariqueter habitat (feed: 86.7%±6.9%; not feed: 81.1%±5.1%) compared to the mud and empty basin (P<0.05) regardless of being fed or not. Habitat had significant effect on mortality (F=27.16, P<0.05), while feeding had and interaction didn’t (F=0.22, P>0.05 and F=1.72, P>0.05). By pairwise comparison, in feeding group, the juveniles were found to show significantly higher mortality in mud (24.4%±1.9%) compared to the S. triqueter (13.3%±3.3%) and empty basin (14.4%±1.9%). In the non-feeding group, the juveniles had in significantly higher mortality in mud (26.6%±5.7%) compared to the empty basin (17.7%±1.9%) and S. triqueter (10.0%±3.3%). The results showed that the larvae of E. sinensis showed preference for vegetation habitats such as S. mariqueter, which may be related to the shelter provided by vegetation. The results of this study indicate the importance of vegetation habitat for the larval stage of E. sinensis, enrich the early life history data, and provide basic reference for resource conservation and habitat restoration.

Abstract:In order to explore the in vitro incubation technique of fertilized eggs of Portunus trituberculatus, this study firstly screened the most suitable isolation solution for fertilized egg blocks, then conducted in vitro incubation studies of fertilized eggs at different developmental stages and transmission electron microscopy observation of fertilized egg membranes after treatment with the isolation solution, and finally measured the larval viability of fertilized eggs treated with the isolation solution after hatching. The results showed that papain was an ideal separation solution, and the separation rate was more than 99% with a concentration of 0.09 g/mL and separation time at 30 min. The highest hatching rate of 89.0%±3.3% was recorded for in vitro embryos in zoea stage, compared to 70.0%±4.8% for the control group. The lowest hatching rate for in vitro embryos was observed at the cleavage stage, which was 58.0%±3.9%, and that for the control group was 31.0%±2.3%. In general, compared with the control group, the hatching rate of the treatment group increased significantly; the observation results of transmission electron microscopy also supported this phenomenon with the structure of fertilized egg membrane being loose and its thickness decreased after the separation solution treatment; exposure to air, formalin solution stress and behavioral test were used to evaluate the quality of larvae in different treatment groups. The results showed that there was no significant difference in the vitality of larvae in treatment group and control group. In conclusion, the isolation solution obtained in this study can effectively improve the hatching rate of fertilized P. trituberculatus eggs without affecting the larval vitality, and our results can provide a reference for the in vitro embryos hatching of P. trituberculatus and other crustaceans.

Abstract:Pacific abalone (Haliotis discus hannai) is an important marine shellfish in China, which is naturally distributed in the coastal areas of Shandong Peninsula and Liaodong Peninsula, and has high economic and nutritional value. Since the 1990s, with the extensive application of hybridization technology, the cultivation industry of H. discus hannai has gradually moved from northern to southern China and developed rapidly. In 2019, the production of H. discus hannai and its hybrid offsprings in China has reached 180 000 tons. However, the process of artificial breeding and selection may reduce the genetic diversity index of species, change the genetic structure, or even cause genetic differentiation of populations. In order to explore the possible effects of cultivation patterns on the genetic structure of Pacific abalone in China in the last 30 years, 259 individuals were collected from Dalian (DL), Rongcheng (RC), Zhangzhou (ZZ), Tuoji Island (TJ), Daqin Island (DQ), and Nanhuangcheng Island (NH), the last three island belonging to the Changshan Archipelago of China. The mitochondrial cytochrome C oxidase subunit (COⅠ) gene and cytochrome B (Cytb) gene sequences were amplified by polymerase chain reaction (PCR) and sequenced on an automatic sequencer by using forward and reverse primers. Bioedit 7.0.5, DNAsp 5.10, MEGA 6.06 and Arlequin 3.5 software were used for sequence analysis. After sequence matching and shearing, 730 bp fragment length of COⅠ and Cytb genes were obtained. The results showed that 48 mutation sites and 30 haplotypes were detected in the 730 bp COⅠ sequence of 259 individuals; the haplotype diversity of the 6 populations ranged from 0.586 to 0.897, and the nucleotide diversity was 0.0056-0.0081; 59 mutation sites and 32 haplotypes were detected in the 730 bp Cytb sequence of 259 individuals. The haplotype diversity ranged from 0.605 to 0.909 and the nucleotide diversity was 0.0077-0.0120 in the 6 populations. The results of F_st and AMOVA among populations based on COⅠ and Cytb genes showed that there was significant genetic differentiation between most populations, and the genetic variation mainly existed between individuals but within populations. The current cultivation mode of H. discus hannai enhanced the gene exchange between different populations, and the secondary contact of populations with different genetic backgrounds resulted in high haplotype diversity and nucleotide diversity in all 6 populations. Different breeding standards in different breeding populations may be an important reason for the significant genetic differentiation. The evaluation of genetic resources of six Haliotis discus hannai populations in the northern and southern China coasts conducted in this paper provides a scientific basis for the rational utilization of the resources in China and the influence of breeding modes on genetic structure.

Abstract:The Pacific oyster (Crassostrea gigas) is one of the most widely farmed shellfish species in the world. With the rise in market demand for in-shell oysters, shell color trait is increasingly of interest to the breeding industry and has been a target trait for selection. In our previous breeding process, an improved orange shell line of C. gigas with a unique shell color was established by the means of hybridization and mass selection. However, the genetic parameters for shell color trait and their correlation with growth traits for the improved orange-shell line remains undocumented. This study aims to estimate genetic parameters (heritability and correlations) for C. gigas at 10 months of age by applying mixed-family approach combined with a nested mating design and CVS imaging system. In this study, heritability for shell color-related traits was estimated in the improved orange shell line of C. gigas by fostering a single cohort of 48 families consisting of 16 sires and 48 dams. A total of 863 offspring were harvested at 10-month age. Pedigree was reconstructed with 12 microsatellite markers. The shell color parameters of selected oysters were measured based on the computer vision system and Lab colorimetric system. REML based on the animal model was used to estimate the genetic parameters of orange shell color traits and correlation with growth traits of C. gigas. The results of parentage assignment showed that 98.61% of the oysters were unambiguously assigned to single parent pairs. Unbalanced contributions of parents were found among families and parents. Coefficients of variation of the progeny were 16.51%-39.62% for growth traits, and 3.70%-43.32% for shell color parameters, suggesting that there was great genetic variation among growth traits. Heritabilities of L^*, a^*, b^*, and ΔE were 0.17±0.07, 0.47±0.23, 0.42±0.21, and 0.56±0.29, respectively. The phenotypic correlations and genetic correlations of L^*, a^*, b^* and ΔE were with the ranges of –0.4-0.48 and –0.79-0.86, respectively. The phenotypic correlations and genetic correlations between the growth traits and shell color traits were low, ranging from –0.04-0.11 and –0.33-0.17 respectively. These results indicated that the breeding population had considerable additive genetic variation in orange shell color traits, and the ongoing selective breeding program should produce considerable genetic improvement in the orange shell color traits of C. gigas. However, indirect selection of growth traits using the shell color trait is infeasible due to their low correlations. Only when both the shell color traits and growth traits were selected as the targets of selective breeding, the traits could be improved. Furthermore, our studies confirmed the feasibility of the posteriori family reconstruction based on molecular markers in a communal rearing environment. The present study provides important information for future selective breeding programs for C. gigas with orange shell color trait.

Abstract:In order to explore the characteristics of waste collection in the octagonal aquaculture tank under the action of submersible flow propellers, this paper uses the method of physical model test to study the different deployment angle θ and the installation distance ratio d/a of the submersible flow propellers (the perpendicular bisector pattern: d1 is the distance between the midpoint of the impeller axis of the propeller and the nearest tank wall, a1 is the length of the long side of the octagonal culture tank; the diagonal pattern: d2 is the midpoint of the impeller axis of the propeller and the nearest short side, a2 is the distance between the sewage outlet of the octagonal aquaculture tank and the nearest short side), the number of flow propellers n and the influence of the layout mode on the collection of waste in the octagonal aquaculture tank. In the experiment, a high-definition camera was used to record the distribution of waste in the culture tank, and MATLAB was used to analyze and calculate the distance between the waste and the center of the tank. In the test, by comparing the maximum value of the distance between the waste and the center of the tank under different working conditions, the pros and cons of the waste collection performance of the aquaculture tank were measured. The results show that the deployment angle θ of the submersible flow propeller, the installation distance ratio d/a, the number of flow propellers n and the arrangement mode all affected the effect of the accumulation of waste in the aquaculture tank; when the deployment angle θ of the device was 45°, the waste collection effect was the best, and when the deployment angle θ was greater than 70°, with the increase of the layout angle, there would be dead corners of waste collection around the octagonal aquaculture tank, the distance between the residual bait and the feces from the center of the sewage outlet increased, and the degree of feed dispersion also become larger; under the working conditions of 30°, 40°, 45°, and 50°, the effect of waste accumulation gradually increased with the increase of the installation distance ratio d/a. When the installation distance ratio is 1/2, the waste collection effect is the best. The waste collection performance of the aquaculture tank increased with the increase of the number of submersible flow propellers, especially when the number of submersible flow propellers increased from 1 to 2. However, after the continuous increase, the waste collection performance was no longer significantly improved. Under equal conditions, the waste collection performance of the aquaculture tank in the diagonal layout mode was obviously better than that in the perpendicular layout mode. The research results can provide basis and guidance for the layout of submersible flow propellers in octagonal aquaculture tanks.

Abstract:Shrimp white feces syndrome (WFS) was highly infectious and causes huge economic losses in shrimp aquaculture industry worldwide. In this study, the relationship between the occurrence of WFS in pond culture Litopenaeus vannamei and environmental factors, microbial factors, host immunity and water microbial community composition were analyzed. Measures including water environment factors, culturable bacteria in shrimp hepatopancreas and water, immune activity in shrimp muscle and microbial community structure in water were detected. Compared with the healthy group, the fluctuation trend of water temperature, dissolved oxygen (DO), pH, salinity and other physical and chemical factors in the diseased pond was similar, they were 26.1-29.0 °C, 4.26-6.08 mg/L, 8.39-8.73, 40-49, and DO and salinity were higher than those in the healthy group. The number of culturable bacteria and Vibrio spp. in hepatopancreas of the healthy shrimp were 1.19×10⁵-7.70×10⁵ CFU/g and 8.80×10³-1.96×10⁴ CFU/g, and the proportion of Vibrio spp. was 2%-16%. Furthermore, the number of culturable bacteria and Vibrio spp. in hepatopancreas of the diseased shrimp were 3.80×10⁵-2.51×10⁶ CFU/g and 2.02×10⁵-1.49×10⁶ CFU/g, the proportion of Vibrio spp. was 55%-70%, the number of Vibrio spp. was 15-113 times higher than that of healthy group. The activities of AKP, ACP, LZM, SOD and PO were 1.21-5.64, 9.17-15.25, 3.56-7.43, 4.83-6.70 and 3.10-4.55 U/mg in healthy shrimp muscles, and 2.12-5.39, 19.22-26.96, 19.73-26.85, 3.00-4.14 and 7.76-9.21 U/mg in diseased shrimp muscles. Comparative analysis showed that the occurrence of WFS was correlated with culturable bacteria, the proportion of Vibrio spp., ACP, LZM, and PO. Microbial community structure analysis showed that the Ace and Chao indices of water bacteria structure in the diseased group showed a certain degree of downward trend, and the PCoA index was high. The relative abundance of Actinomycetota and Proteobacteria decreased, and the relative abundance of Bacteroidetes and Cyanobacteria increased significantly in diseased group. RDA analysis showed that salinity, DO, culturable bacteria in shrimp hepatopancreas and water and culturable Vibrio spp. in shrimp hepatopancreas were the main factors influencing the microbial community structure in the water. The results indicated that the occurrence of WFS is affected by pathogen, body immunity and water microbial community composition, which provides data support for further pathogenic analysis of shrimp WFS, and establishes the theoretical basis for the prevention and control of WFS. The occurrence of aquatic diseases is the result of the comprehensive action of environmental factors, pathogenic microorganisms and host autoimmune ability. Comprehensive analysis of the pathogen of WFS, host immunity and changes in the structure of bacteria in water environment from the production practice is of great significance to explore the related factors of WFS occurrence and comprehensive control. It not only deepens the thinking of studying the occurrence of WFS from multiple perspectives, but also provides valuable information for strengthening the healthy cultivation of L. vannamei.

Abstract:Superoxide dismutase (SOD) is one of the main antioxidant enzymes, and its expression level may be significantly affected by environmental and biological stimuli. Therefore, SOD is considered as an important component of invertebrate innate immunity, though the mechanism of its contribution to immune responses is rarely reported. In this study, we cloned the cytoplasmic manganese SOD of Macrobrachium rosenbergii (MrcMnSOD), prepared its polyclonal antibodies, and analyzed its expression pattern under Aeromonas hydrophila infection. The results showed that A. hydrophila infection significantly increased the expression of MrcMnSOD both on the transcription level and protein level. In order to explore the possible mechanism of MrcMnSOD involvement in the immune response, further antibacterial assays were conducted. The results showed that MrcMnSOD can significantly inhibit the growth of three gram-negative bacteria (Escherichia coli, Vibrio parahaemolyticus, A. hydrophila) and two gram-positive bacteria (Streptococcus agalactiae, Staphylococcus aureus), and the inhibitory effect is largely irrespective of protein concentration. The present study indicates that MrcMnSOD may participate in the immune response as an immune-related molecule. This study reportes the immunobiological function of MrcMnSOD preliminarily, aiming to lay the relevant foundation for further research on SOD.

Abstract:Caulerpa lentillifera is a kind of perennial large edible seaweed, which is also known as "sea grape" because of its upright stem globule glittering and translucent, similar in appearance to grapes. C. lentillifera is also one of the most suitable seaweeds for human consumption. It is rich in nutrients and contains a variety of amino acids, vitamins, polysaccharides and fatty acids needed by the human body. Among them, polysaccharide is the most important active component in C. lentillifera. According to research, the crude polysaccharide content of C. lentillifera accounts for 34.00%-64.97% of its dry weight, which is higher than that of most edible algae, such as Scagassum, Hizikia fusifarme and Undaria pinnatifida. At present, the main extraction methods for polysaccharides of C. lentillifera are water extraction, alkali extraction and ultrasonic-assisted extraction, and the extraction rate is 3.22%-11.30%, but there are still a large amount of polysaccharides that remains un-extracted. In order to develop a mild, efficient and low-cost extraction process of polysaccharides from C. lentillifera, and to explore the antioxidant activity of the polysaccharide, we screened five existing extraction methods of polysaccharides from C. lentillifera. Through single factor experiment and response surface experiment, the ratio of material to solution, extraction temperature, extraction time, amount of papain and extraction times were optimized, and the optimum process parameters were obtained. Polysaccharide concentration was determined by anthrone sulfate method in the experiment. In addition, we investigated the scavenging activity of the polysaccharide on DPPH and ABTS free radicals. The results showed that adding papain is the most efficient method to extract polysaccharides from C. lentillifera. The order of the factors affecting the extraction rate of polysaccharide from C. lentillifera is as follows: ratio of material to solution > extraction temperature > extraction time, and the ratio of material to solution showed an extremely significant influence on the extraction rate of the polysaccharide (P<0.001). The best extraction parameters after optimization were as follows: ratio of material to solution is 1∶45, extraction temperature 60 ℃, extraction time 3 h, extraction count 2 times, the addition amount of papain 2.0%. Under this condition, the extraction rate of polysaccharides can reach 41.24%±0.09%. In addition, polysaccharides from C. lentillifera had good scavenging activities on DPPH and ABTS free radicals, and their IC₅₀ values were 2.32 and 0.67 mg/mL, respectively. This study shows that the optimized papain enzymatic hydrolysis can improve the extraction rate of polysaccharides from C. lentillifera effectively, among which the ratio of material solution is the most important factor affecting this method. Besids, the polysaccharides of C. lentillifera have good antioxidant activity.